Intra-Operative Electron Radiation Therapy (IOERT) is a treatment by which electron radiation is applied directly to a residual tumor or tumor bed during cancer surgery. Electron beams have been deemed useful for intraoperative radiation treating because, depending on the electron energy, the dose falls off rapidly below a target site, thereby sparing underlying healthy tissue. During IOERT, a physician has direct visualization of the tumor, can exclude normal tissue from the field, and can also protect critical structures within the field and underlying the target volume. IOERT can be administered at the time of surgery when microscopic residual tumor cells are most vulnerable to destruction.
While still in the research stages for breast cancer, IOERT has already become standard treatment for certain types of cancer, such as advanced pelvic and abdominal tumors, sarcoma and colorectal cancers.
Mobetron® radiation therapy machines are used to administer single intraoperative doses of radiation to a patient undergoing tumor excision. To change the effective depth of dose administered by a Mobetron® radiation therapy machine, an operator would change the machine beam energy. A Mobetron® machine reportedly weighs ⅛ the weight of a conventional electron linear accelerator and can be fitted into any operating theater, requiring no room shielding. The physical dimensions and weight of one such Mobetron® machine are as follows: 82 inches in length; 42.7 inches in width; 99.5-111 inches in maximum or operating height; 78 inches in minimum or stowed height; and 2,937 pounds in total weight. For transport, a special jack is used which extends the length of the Mobetron® machine to 95 inches. After a surgical team has completed excision of all visible positive tissue, the Mobetron® machine's applicator is placed within the surgical site as close as possible to the suspected microscopic cancerous tissue to be treated.
The Mobetron® machine has a fixed electron beam head, which moves vertically and can be tilted. This design has limited provision for stowing the head and is relatively large and bulky.
The present invention addresses this drawback by providing an electron therapy unit for delivering therapeutic electrons to a patient during an operation that comprises a movable and stowable beam head that may be connected permanently or temporarily to either (i) a transportable base cabinet, or (ii) a fixed structure, using one or more optionally pivotable arms. The beam head can be moved from a stowed position on either the base cabinet or fixed structure to an operating position over a patient.
In a first exemplary embodiment, the inventive electron therapy unit is a mobile unit suitable for in-hospital use or for shared use between hospitals or clinics where the beam head is connected permanently or temporarily to a transportable base cabinet. The unit is self-contained, small, light and easy to use. It has a very reliable, compact design, allowing for easy stowing to a small rugged configuration for transport.
The inventive unit in this first exemplary embodiment offers size and weight reduction over the Mobetron® machine. In particular, in a preferred embodiment the stowed configuration of the inventive unit has:                an overall height ranging from about 68 inches to about 95 inches (more preferably, from about 65 inches to about 90 inches);        an overall width ranging from about 30 inches to about 45 inches (more preferably, from about 30 inches to about 40 inches);        an overall depth ranging from about 45 inches to about 60 inches (more preferably, from about 46 inches to about 50 inches); and        a total weight ranging from about 600 pounds to about 800 pounds (more preferably, from about 400 pounds to about 500 pounds).        
In a second exemplary embodiment, the inventive electron therapy unit is a stationary unit where the beam head is connected permanently or temporarily to a fixed structure. As will be explained in greater detail below, in this embodiment, the beam head and a modulator are separate from the base cabinet, with the base cabinet containing control electronics, a control computer, and a temperature control unit (TCU).
In a first preferred embodiment, the beam head contains electron beam producing means in the form of a radio-frequency (RF) source and RF components and is attached to either the base cabinet or fixed structure using one or two pivotable arms.
In a second preferred embodiment, the beam head does not contain RF components. Instead, the RF components are contained within the base cabinet and microwave power is carried to the RF source within the beam head through a waveguide in one of the pivotable arms.
In a third preferred embodiment, an arm with a rotating joint is used to connect the beam head to either the base cabinet or fixed structure, while in a fourth preferred embodiment, a rotating joint is used to connect the arm to either (i) the beam head or (ii) the base cabinet or fixed structure, or both (i) and (ii).
In a fifth preferred embodiment, RF components are contained in the base cabinet, and microwave power is carried to the RF source within the beam head through a flexible waveguide.
In a sixth preferred embodiment, the RF source is an RF based linear accelerator, the RF components include an electron gun for producing and delivering a stream of electrons to the linear accelerator, and a direct current (DC) power supply is used for the electron gun. The DC power supply operates at a voltage less than 35 kilovolts, preferably less than or equal to about 5 kilovolts.
The present invention further provides a method for reducing or eliminating the possibility of significantly higher current caused by electrical arcs and power excursions during operation of the inventive electron therapy unit, where the RF source is an RF based linear accelerator, and the RF components include an electron gun for producing and delivering a stream of electrons to the linear accelerator, the method comprising using a DC power supply for the electron gun, the DC power supply operating at a voltage less than 35 kilovolts, preferably less than or equal to about 5 kilovolts.
The present invention further provides an ion chamber for use with an electron therapy unit, and an electron therapy unit that employs such an ion chamber. The ion chamber comprises two or more collector (i.e., signal) plates and associated bias plates, each having a centrally located hole that extends through the plate.
The present invention also provides a method for minimizing electron beam scattering and x-ray generation in an electron therapy unit, the method comprising:
reducing pulse current and pulse repetition rate; and
using the ion chamber described above on or within the beam head.
Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.